Because the aorta is the main artery carrying blood from the heart to the rest of the body, an aneurysm in this artery, called an aortic aneurysm, is especially serious. The bursting of this main artery can be fatal unless it's treated immediately. An aortic aneurysm larger than about 4 cm. in diameter in this section of the aorta is ominous. Left untreated, the aneurysm may rupture, resulting in rapid, and usually fatal, hemorrhaging.
For reconstruction of essential vessels such as the aorta, surgical restoration is extremely life-threatening. Surgical methods entail significant surgery in which an artificial section of vessel is implanted into the diseased or impeded lumen. The weak portion of the lumen may be surgically separated and an artificial graft stitched to the ends of the vessel.
Other devices for the repair of vessels such as arteries include a NITINOL® coil with a graft. The NITINOL® coil is diminished in proportion as it cools. When arranged in the body, its temperature increases, and it returns to a preferred dimension to clamp a graft within the lumen of the vessel. These devices are detailed in Charles T. Dottner, et al., Transluminal Expandable Nitinol Coil Stent Grafting: Preliminary Report, Radiology 147:259-260, April 1983, and Andrew Cragg, et al., Nonsurgical Placement of Arterial Endoprostheses: A New Technique Using Nitinol Wire, Radiology 147:261-263, April 1983.
While some aneurysms cause no noticeable symptoms, others cause chest or back pain. Often an aneurysm first shows up on a chest X-ray. The stent and location of the aneurysm can be estimated through echocardiography or through radiological imaging—either magnetic resonance imaging (MRI) or computed tomography (CAT or CT) scanning. Patients who are found to have small aneurysms can be monitored and examined regularly, but those with large or dissecting ones need prompt treatment, because the rupture of an aneurysm can be fatal.
Description of the prior art includes such devices as intravascular devices, called “stents”, which are placed in the organism by means of mechanical placement on balloons or other types of catheters. Catheters are a type of tubular metal or rubber instrument designed to pass through canals such as arteries.
The accepted surgical technique of eradicating the aneurysm and replacing the weakened area with a prosthetic graft has been continuously improved over the years.
The use of prior art still causes a relatively high mortality rate for patients undergoing the surgery. One reason for the high fatality rate is that the procedure constitutes a major surgical endeavor, making it highly elective in patients with severe coronary or cerebral arteriosclerosis, severe confining pulmonary disease, consequential renal disease or other complicating factors. Consequently, even though particular techniques have been advanced recently that elude or reduce the stress, morbidity, and risk of mortality associated with surgical intervention to repair aortic aneurysms, the methods that have been perfected do not effectively treat the aneurysm. These methods also do not eliminate the influenced section of aorta from the pressures and stresses associated with the circulation. The devices disclosed in the prior art do not furnish a reliable and quick means to bypass an aneurysmal artery.
Prior art also relates to prostheses consisting of two attachment means, or stents, connected by means of a flexible coaxial tube, which is implanted along the arterial zone influenced by the aneurysm. The ideal material used for stents should include fundamentally the following characteristics: it should not have any toxic, allergic or carcinogenic action, and should be pathologically inert. The stent should be tolerated by the organism: it should have an elevated degree of elasticity. It should also allow host fibroblasts to pierce the thickness of the prosthesis wall by adhering to the surrounding tissues.
Correspondingly, inside the vessel channel, the cells coming from the blood can adhere to the surface and arrange a layer defined as neointima. Furthermore, it is necessary that the prosthesis material can be submitted to the various sterilization procedures without losing its properties and can be easily shaped. Occasionally, the prosthesis detaches in the suture, thus causing the formation of scar tissue that, by collapsing due to the blood pressure, causes a pseudoaneurysm, which in turn, causes the prosthesis end to come off the artery end to which it was associated. Vascular prostheses have been used to accomplish bypass operations and to repair damaged vessels in the body such as arteries and veins.
Often, a piece of one's own vessel is taken from another part of the body to form the prosthesis. This involves putting the patient through an additional surgical operation. In addition, in many patients, suitable vessels are not available.
In one type of pathology, a layer of expanded scar tissue forms around the prosthesis; thereby the arterial blood laminar flow becomes vertical which produces thrombi stratification within the scar tissue.
These stents, used as a means of attachment for intravascular prostheses, can be deformed by enlarging their diameter when subjected to enlargement from inside by inflation of a balloon, until they are restrained against the internal side of the arterial wall. An alternative method of delivery properties to the body which have a tendency to take a radially enlarged position is to attach the elements to each other at the points of crossing in a suitable manner, for example, by some form of welding, gluing or similar occurrence.
With the current balloon catheter devices, the attachment of stents on ends of the prosthesis is an exhausting, dangerous and time-consuming procedure. Prior art includes using the femoral artery to insert these rigid and cumbersome intra-aortic balloon catheters because of the large diameter of that artery. Nonetheless, substantial surgery must be performed in order to reach and isolate the femoral artery.
In addition, a large incision must be made in the femoral artery wall to allow introduction of these prior art devices. The safety of intra-aortic balloon pumping using the catheters of the prior art has been controversial since they can bring about, and in some instances have caused, aortic dissections, punctures and trauma chiefly because of the proportionate stiffness of the devices.
Furthermore, this stiffness prevents precise maneuverability of the catheter within the vascular shape and consequently restricts its chances of effectiveness. It is acknowledged in the prior art that insertion and controlling of catheters is complicated and that trauma and injury to the incision and blood vessel may occur during the insertion and controlling of the catheter.
The technique of the introduction of catheters with inflatable balloons is known as valvuloplasty and angioplasty treatments, in which dilation catheters for one or more lumina are used. If it is desired to implant a prosthesis of a type mentioned above with the current dilation catheters, the catheters consist of two attachment means or stents. The stents are coaxially connected together by means of a flexible tube. It is necessary to use two catheters, one at a time, to consecutively dilate the proximal stent and the distal stent. This maneuver is difficult, risky and time-consuming, and is not recommended.
Prior art also includes a method of repairing arteries, which involves inserting the stent device (stainless steel wire about 0.018 in.) through the groin, and using it to patch the aneurysm. This was determined a significant proposition and would exclude the need for more invasive and risky surgery inside the abdomen. The suffering and jeopardy to life ordinarily associated with aortic aneurysms demands surgical remedy in a preponderance of situations. Prior art also includes methods of using devices for the repair of lumens such as blood vessels and arteries by use of a NITINOL® (nickel-titanium alloy) coil with a graft. The NITINOL® coil is reduced in dimension as it cools and then the coil is heated to change its dimensions. Ordinarily acknowledged manners of execution can be the basis of consequential trauma to the patient.
Also, existing methods allow a grafting system that provides catheter-based delivery and implantation of a specialized, sutureless prosthesis to repair abdominal aortic aneurysms. The prior art procedure is traumatic to the patient, often causes major surgery, and may be dangerous or impossible to perform if, as is not infrequent, the health of the patient is poor.
Aneurysm surgery has been performed for approximately fifty years. The accepted surgical procedure of eradicating the aneurysm and replacing the weak artery or vein surface with a prosthetic graft has been constantly refined. Even so, the fatality rate for patients enduring the surgery is still seriously elevated. One reason for the high fatality rate is that the procedure presents a significant surgical endeavor, making it enormously discretionary in patients with severe coronary or cerebral arteriosclerosis.
The two most widely used approaches are resection of the aneurysm or the performing of an axillobifemoral bypass occurring with the coagulated process of the aneurysm repair.
The axillobifemoral bypass method leaves the aneurysm open at the proximal end. The danger of this procedure is that the clot of an infra-renal aneurysm may propagate over the renal arteries causing loss of blood flow to the kidneys and possibly resulting in renal failure.
Additionally, the grafted artery placed during the procedure is adjacent the exterior of the skin where it is receptive to injury. The considerable rerouting completed by the bypass may also cause complications. Present treatments are considerably invasive; many times a patient consequently expires during the repair operation.
The resection method requires a large surgical opening into the abdominal cavity with surgical penetration of a prosthetic graft inside the flawed segment. The surgical invasion of the abdominal cavity greatly increases the complications and mortality of procedure, especially with respect to the majority of those patients with such aneurysms that also exhibit other reasons for hospitalization.
Another major disadvantage of presently accepted eradication aneurysm surgical techniques is that because of the severe nature of the operation, it can be performed only in sophisticated medical centers having the potential to carry out superior cardiovascular surgery. If the prognosis is not made until the diagnosis for a rupture is determined, mortality has been known to occur because of the unsatisfactory amount of time to transfer the patient to a major medical center where remedial operation could be discharged.
Choudhury (e.g., see U.S. Pat. No. 4,140,126) proposed a less invasive surgical procedure. This method comprises a procedure for restoring an aortic aneurysm using a catheter inserted into the femoral artery and transferred to the site of the aneurysm. The only incision required is proportionately small and is fashioned in the leg of the patient. The catheter maintains a pair of expanding rings spaced barely more than the length of the aneurysm. Many mooring pins, which extend radically of the catheter, are attached to the rings.
The prosthetic graft is held by the mooring pins in a collapsed position smaller than the inside diameter of the artery. Once inserted, the rings are enlarged and the anchoring pins pierce the aortic walls, holding the graft in place with the help of the hemodynamic pressure of blood in the aorta.
The Choudhury method, while much less invasive than the generally accepted surgical techniques, has several particular drawbacks. The anchoring pins used to hold the graft in place, first on the catheter and then in the aorta, pierce the aortic wall and may cause consequential impairment to the aorta, particularly near the region of the aneurysm that has already seriously weakened the aorta. The pins do not reliably grip the graft in location within the walls of the aorta. The procedure also is completed while blood continues flowing through the aorta, the aneurysm site, and the femoral artery. The graft of Choudhury expands only a very small distance below the site of the aneurysm; consequently, the area of healthy vessel to which it must become attached is very small, resulting in drainage around the graft or the graft not sticking to the vessel.
Many ruptures have been reported to the FDA worldwide among the roughly 13,500 patients treated with the presently used stent graft. Other problems include: poor placement of the graft, leakage (endoleak), movement or migration of the device after it is implanted and metal frame fractures in the device, suture and fabric tears.
Accordingly, there is a need in the art for less invasive repair procedures for repairing aneurysms and other defects in arteries such as the aorta or other arteries or vessels. There is a continuing need for methods, systems and devices for executing an aneurysm repair, which does not require major surgery and which may be used on higher risk patients than what conventional aneurysm surgery currently allows.